INTRODUCTION. XV 



irritability. The tips of the tentacles are bristled with the 

 minute points, called by Dr. T. S. Wright palpocils* 

 which he considers as delicate tactile organs. These are 

 specially conspicuous on the globose heads of the tentacles 

 of Corynactis and Caryophyllia. I am not sure whether 

 I ought to regard, as an organ of taste, the surface of the 

 lower part of the stomach, which in T. crassicornis I find 

 covered with innumerable papillae, not quite uniform in size 

 or shape, some being more pointed, others more round, and 

 averaging about 0003 inch in diameter. 



4. Digestive System. This is very simple, consisting 

 essentially of a short tube descending from the centre of 

 the disk, with an open extremity hanging loose in the 

 body-cavity (Plate XI. fig. 1, c). I have already observed 

 that the inner edges of the septa are inserted into its outer 

 wall, and these maintain it in place, while by their trans- 

 verse contraction they can draw asunder its surfaces, and 

 by their longitudinal contraction they can either lengthen 

 or shorten it. The stomach-wall itself, however, is muscular ; 

 possessing at least the layer of transverse fibres, though I 

 have not quite satisfied myself of the presence of the longi- 

 tudinal layer. 



The form of the stomach is not that of a cylinder, but of 

 a flattened sac, or of a pillow-case unsewed at both ends. 

 This form may be well seen in pellucid specimens of A. 

 dianthus, and in the smaller Ilyanthid^e, and it may be 

 examined by dissection in others. The excessive contrac- 

 tion of the parts, and the copious excretion of mucus, do, 

 however, present great obstacles to satisfactory demonstra- 

 tions under the scalpel. I have therefore resorted to 

 accessory means. A specimen of T. crassicornis fully 

 expanded I treated with laudanum, drop by drop. It 

 immediately expelled the water contained in the tentacles, 

 causing these organs to shrink and shrivel, but not re- 

 tracting them. The mouth, which had been pursed together, 

 began slowly to open, and dilated greatly, almost to the 

 concealment of the tentacles, the summit of the now 

 flattened animal being almost wholly occupied by the 

 gaping orifice. An excellent opportunity was thus afforded 

 for examining the structure of the stomach, which was 

 revealed without the excretion of mucus. The languor, 

 too, induced by the narcotic, allowed the parts to be freely 

 * See Edin. New Phil. Joura., April, 1857. 



